18F-FDG PET and MR imaging associations across a spectrum of pediatric brain tumors: a report from the pediatric brain tumor consortium

The promise of metabolic imaging in diffuse midline glioma

Recent insights into histopathological and molecular subgroups of glioma have revolutionized the field of neuro-oncology by refining diagnostic categories. An emblematic example in pediatric neuro-oncology is the newly defined diffuse midline glioma (DMG), H3 K27-altered. DMG represents a rare tumor with a dismal prognosis. The diagnosis of DMG is largely based on clinical presentation and characteristic features on conventional magnetic resonance imaging (MRI), with biopsy limited by its delicate neuroanatomic location. Standard MRI remains limited in its ability to characterize tumor biology. Advanced MRI and positron emission tomography (PET) imaging offer additional value as they enable non-invasive evaluation of molecular and metabolic features of brain tumors. These techniques have been widely used for tumor detection, metabolic characterization and treatment response monitoring of brain tumors. However, their role in the realm of pediatric DMG is nascent. By summarizing DMG metabolic pathways in conjunction with their imaging surrogates, we aim to elucidate the untapped potential of such imaging techniques in this devastating disease.

Joint EANM/SIOPE/RAPNO practice guidelines/SNMMI procedure standards for imaging of paediatric gliomas using PET with radiolabelled amino acids and [18F]FDG: version 1.0

Positron emission tomography (PET) has been widely used in paediatric oncology. 2-Deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) is the most commonly used radiopharmaceutical for PET imaging. For oncological brain imaging, different amino acid PET radiopharmaceuticals have been introduced in the last years. The purpose of this document is to provide imaging specialists and clinicians guidelines for indication, acquisition, and interpretation of [18F]FDG and radiolabelled amino acid PET in paediatric patients affected by brain gliomas. There is no high level of evidence for all recommendations suggested in this paper. These recommendations represent instead the consensus opinion of experienced leaders in the field. Further studies are needed to reach evidence-based recommendations for the applications of [18F]FDG and radiolabelled amino acid PET in paediatric neuro-oncology. These recommendations are not intended to be a substitute for national and international legal or regulatory provisions and should be considered in the context of good practice in nuclear medicine. The present guidelines/standards were developed collaboratively by the EANM and SNMMI with the European Society for Paediatric Oncology (SIOPE) Brain Tumour Group and the Response Assessment in Paediatric Neuro-Oncology (RAPNO) working group. They summarize also the views of the Neuroimaging and Oncology and Theranostics Committees of the EANM and reflect recommendations for which the EANM and other societies cannot be held responsible.

The Role of PET in Supratentorial and Infratentorial Pediatric Brain Tumors

OBJECTIVE

This review aims to provide a summary of the clinical indications and limitations of PET imaging with different radiotracers, including 18F-fluorodeoxyglucose (18F-FDG) and other radiopharmaceuticals, in pediatric neuro-oncology, discussing both supratentorial and infratentorial tumors, based on recent literature (from 2010 to present).

METHODS

A literature search of the PubMed/MEDLINE database was carried out searching for articles on the use of PET in pediatric brain tumors. The search was updated until December 2020 and limited to original studies published in English after 1 January 2010.

RESULTS

18F-FDG PET continues to be successfully employed in different settings in pediatric neuro-oncology, including diagnosis, grading and delineation of the target for stereotactic biopsy, estimation of prognosis, evaluation of recurrence, treatment planning and assessment of treatment response. Nevertheless, non-18F-FDG tracers, especially amino acid analogues seem to show a better performance in each clinical setting.

CONCLUSIONS

PET imaging adds important information in the diagnostic work-up of pediatric brain tumors. International or national multicentric studies are encouraged in order to collect larger amount of data.

Metastatic Medulloblastoma: 18F-FDG and 68Ga-DOTANOC PET/CT in Response Evaluation

ABSTRACT

We describe the utility of molecular imaging with 18F-FDG and 68Ga-DOTANOC PET for treatment response assessment in a case of metastatic medulloblastoma. 18F-FDG and 68Ga-DOTANOC PET/CT revealed extensive metastases to bone and bone marrow. Patient subsequently had an excellent response to systemic chemotherapy which was evidenced by resolution of tracer-avid skeletal lesions on both FDG and DOTANOC PET/CT.

Utilidad de la tomografía por emisión de positrones/tomografía computada (PET/CT) en pacientes con diagnóstico de meduloblastoma

"PET/CT (positron emission tomography/computed tomography, for its acronym in English) is a unique imaging method that provides in vivo evidence of both biochemical and physiological activities of the brain, spinal cord and tumors that involve these structures. Medulloblastoma is the most common malignant tumor of the central nervous system (CNS) in pediatric patients, so PET/CT plays an important role as it provides information on the grade and extent of the tumor as well as to determine the appropriate site for the biopsy, assessing the response to the treatment and the patient’s prognosis. There are different radiopharmaceuticals for the evaluation of central nervous system tumors, but 18F FDG (Fluor-2-fluoro-2-desoxy-D-glucose) and 68Ga-DOTA-NOC (68Ga-DOTA0-1NaI3-octreotide) have been studied to help us evaluate and follow up patients diagnosed with medulloblastoma. Medulloblastoma has an overexpression of glucose transporters, mainly type 1, and an overexpression of predominantly type 2 somatostatin receptors, which allows a high affinity for these radiopharmaceuticals. Key words: Medulloblastoma; positron emission tomography; PET/C; 18F-FDG; 68Ga-DOTA-NOC; brain tumor.

Differential Expression of Mitochondrial Biogenesis Markers in Mouse and Human SHH-Subtype Medulloblastoma

Medulloblastoma is a brain tumor that arises predominantly in infants and children. It is the most common pediatric brain malignancy. Around 25% of medulloblastomas are driven by constitutive activation of the Hedgehog signaling pathway. Hedgehog-driven medulloblastoma is often studied in the laboratory using genetic mouse models with overactive Hedgehog signaling, which recapitulate many of the pathological features of human Hedgehog-dependent tumors. However, we show here that on a molecular level the human and mouse HH-dependent MB are quite distinct, with human, but not mouse, tumors characterized by the presence of markers of increased oxidative phosphorylation and mitochondrial biogenesis. The latter suggests that, unlike for many other types of tumors, a switch to glycolytic metabolism might not be co-opted by human SHH-MB to perpetuate their survival and growth. This needs to be taken into consideration and could potentially be exploited in the design of therapies.

18F-FDG PET-CT in paediatric oncology: established and emerging applications

Accurate staging and response assessment is vital in the management of childhood malignancies. Fluorine-18 fluorodeoxyglucose positron emission tomography/CT (FDG PET-CT) provides complimentary anatomical and functional information. Oncological applications of FDG PET-CT are not as well-established within the paediatric population compared to adults. This article will comprehensively review established oncological PET-CT applications in paediatric oncology and provide an overview of emerging and future developments in this domain.

Embryonal Tumors of the Central Nervous System: From the Radiologic Pathology Archives

Embryonal tumors of the central nervous system (CNS) are highly malignant undifferentiated or poorly differentiated tumors of neuroepithelial origin and have been defined as a category in the World Health Organization (WHO) classification since the first edition of the "Blue Book" in 1979. This category has evolved over time to reflect our ever-improving understanding of tumor biology and behavior. With the most recent update in 2016, many previous histologic diagnoses incorporate molecular parameters for the first time (genetically defined entities). While medulloblastoma and atypical teratoid/rhabdoid tumor are familiar carryovers from the 2007 CNS WHO classification, there are major changes to the embryonal tumor category: for example, elimination of the term CNS primitive neuroectodermal tumor and addition of a new genetically defined entity, embryonal tumor with multilayered rosettes, C19MC-altered. The purpose of this article is to discuss both the radiologic-pathologic features of CNS embryonal tumors and the new molecularly defined types/subtypes that will become the standard classification/terminology for future diagnoses and tumor research.

Evaluation of 11C-Methionine PET and Anatomic MRI Associations in Diffuse Intrinsic Pontine Glioma

The role of metabolic imaging in the diagnosis, treatment, and response assessment of diffuse intrinsic pontine glioma (DIPG) is poorly defined. We investigated the uptake of ¹¹C-methionine in pediatric patients with newly diagnosed DIPG and evaluated the associations of ¹¹C-methionine PET metrics with conventional MRI indices and survival outcomes. Methods: Twenty-two patients with newly diagnosed DIPG were prospectively enrolled on an institutional review board-approved investigational study of ¹¹C-methionine PET. All patients underwent baseline ¹¹C-methionine PET/CT, and initial treatment-response scans after chemotherapy or radiation therapy were obtained for 17 patients. Typical and atypical DIPGs were assessed clinically and radiographically and defined by multidisciplinary consensus. Three-dimensional regions of interest, reviewed by consensus between a nuclear medicine physician and a radiation oncologist, were delineated after coregistration of PET and MR images. Associations of ¹¹C-methionine uptake intensity and uniformity with survival, along with associations between ¹¹C-methionine uptake and conventional MRI tumor indices over time, were evaluated. ¹¹C-methionine PET voxel values within regions of interest were assessed as threshold values across proportions of the study population, and ¹¹C-methionine uptake at baseline was assessed relative to MRI-defined tumor progression. Results: ¹¹C-methionine uptake above that of uninvolved brain tissue was observed in 18 of 22 baseline scans (82%) and 15 of 17 initial response scans (88%). ¹¹C-methionine avidity within MRI-defined tumor was limited in extent, with 11 of 18 positive baseline ¹¹C-methionine PET scans (61%) showing less than 25% ¹¹C-methionine-avid tumor. The increase in total tumor volume with ¹¹C-methionine PET was relatively limited (17.2%; interquartile range, 6.53%-38.90%), as was the extent of ¹¹C-methionine uptake beyond the MRI-defined tumor (2.2%; interquartile range, 0.55%-10.88%). Although baseline ¹¹C-methionine PET intensity and uniformity metrics did not correlate with survival outcomes, initial ¹¹C-methionine avidity overlapped with recurrent tumor in 100% of cases. A clinical diagnosis of atypical DIPG was associated with borderline significantly prolonged progression-free survival (P  =  0.07), yet ¹¹C-methionine PET indices at diagnosis did not differ significantly between atypical and typical DIPGs. Conclusion: Most newly diagnosed DIPGs are successfully visualized by ¹¹C-methionine PET. Baseline ¹¹C-methionine uptake delineates regions at increased risk for recurrence, yet intensity and uniformity metrics did not correlate with treatment outcomes in children with DIPG in this study.

Primary diffuse large B-cell lymphoma of the choroid plexus: A case report and review of the literature

Background

Primary lymphomas in the choroid plexus are much less frequent than primary lymphomas in the brain parenchyma.

Case Description

A 66-year-old male patient was referred to our department with a right intraventricular mass that had been diagnosed by biopsy at another hospital as anaplastic ependymoma. The patient underwent subtotal removal of the tumor via a transcortical inferior temporal gyrus approach. The mass was attached to the choroid plexus in the right atrium. Histopathological examination showed diffuse large B-cell lymphoma. Ophthalmological examination, blood tests, computed tomography of the whole body, and bone marrow biopsy did not show any other lesion, leading to the diagnosis of primary choroid plexus lymphoma. The patient underwent chemotherapy with three courses of high-dose methotrexate and one course of carboplatin and etoposide followed by whole-brain irradiation (1.8 Gy × 22).

Conclusion

We present a rare case of primary choroid plexus lymphoma, which should be considered in the differential diagnosis of choroid plexus tumors.

Comparison among conventional and advanced MRI, 18F-FDG PET/CT, phenotype and genotype in glioblastoma

Glioblastoma (GB) is a highly heterogeneous tumor. In order to identify in vivo the most malignant tumor areas, the extent of tumor infiltration and the sites giving origin to GB stem cells (GSCs), we combined positron emission tomography/computed tomography (PET/CT) and conventional and advanced magnetic resonance imaging (MRI) with histology, immunohistochemistry and molecular genetics. Prior to dura opening and tumor resection, forty-eight biopsy specimens [23 of contrast-enhancing (CE) and 25 of non-contrast enhancing (NE) regions] from 12 GB patients were obtained by a frameless image-guided stereotactic biopsy technique. The highest values of 2-[18F]-fluoro-2-deoxy-D-glucose maximum standardized uptake value (18F-FDG SUVmax), relative cerebral blood volume (rCBV), Choline/Creatine (Cho/Cr), Choline/N-acetylaspartate (Cho/NAA) and Lipids/Lactate (LL) ratio have been observed in the CE region. They corresponded to the most malignant tumor phenotype, to the greatest molecular spectrum and stem cell potential. On the contrary, apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in the CE region were very variable. 18F-FDG SUVmax, Cho/Cr and Cho/NAA ratio resulted the most suitable parameters to detect tumor infiltration. In edematous areas, reactive astrocytes and microglia/macrophages were influencing variables. Combined MRI and 18F-FDG PET/CT allowed to recognize the specific biological significance of the different identified areas of GB.

Meta-Analysis of the Correlation between Apparent Diffusion Coefficient and Standardized Uptake Value in Malignant Disease

The objective of this meta-analysis is to explore the correlation between the apparent diffusion coefficient (ADC) on diffusion-weighted MR and the standard uptake value (SUV) of ¹⁸F-FDG on PET/CT in patients with cancer. Databases such as PubMed (MEDLINE included), EMBASE, and Cochrane Database of Systematic Review were searched for relevant original articles that explored the correlation between SUV and ADC in English. After applying Fisher's r-to-z transformation, correlation coefficient (r) values were extracted from each study and 95% confidence intervals (CIs) were calculated. Sensitivity and subgroup analyses based on tumor type were performed to investigate the potential heterogeneity. Forty-nine studies were eligible for the meta-analysis, comprising 1927 patients. Pooled r for all studies was −0.35 (95% CI: −0.42–0.28) and exhibited a notable heterogeneity (I² = 78.4%; P < 0.01). In terms of the cancer type subgroup analysis, combined correlation coefficients of ADC/SUV range from −0.12 (lymphoma, n = 5) to −0.59 (pancreatic cancer, n = 2). We concluded that there is an average negative correlation between ADC and SUV in patients with cancer. Higher correlations were found in the brain tumor, cervix carcinoma, and pancreas cancer. However, a larger, prospective study is warranted to validate these findings in different cancer types.

Brain Tumors: An Update on Clinical PET Research in Gliomas

A previous review published in 2012 demonstrated the role of clinical PET for diagnosis and management of brain tumors using mainly FDG, amino acid tracers, and ¹⁸F-fluorothymidine. This review provides an update on clinical PET studies, most of which are motivated by prediction of prognosis and planning and monitoring of therapy in gliomas. For FDG, there has been additional evidence supporting late scanning, and combination with ¹³N ammonia has yielded some promising results. Large neutral amino acid tracers have found widespread applications mostly based on ¹⁸F-labeled compounds fluoroethyltyrosine and fluorodopa for targeting biopsies, therapy planning and monitoring, and as outcome markers in clinical trials. ¹¹C-alpha-methyltryptophan (AMT) has been proposed as an alternative to ¹¹C-methionine, and there may also be a role for cyclic amino acid tracers. ¹⁸F-fluorothymidine has shown strengths for tumor grading and as an outcome marker. Studies using ¹⁸F-fluorocholine (FCH) and ⁶⁸Ga-labeled compounds are promising but have not yet clearly defined their role. Studies on radiotherapy planning have explored the use of large neutral amino acid tracers to improve the delineation of tumor volume for irradiation and the use of hypoxia markers, in particular ¹⁸F-fluoromisonidazole. Many studies employed the combination of PET with advanced multimodal MR imaging methods, mostly demonstrating complementarity and some potential benefits of hybrid PET/MR.

A 32 mm × 32 mm × 22 mm monolithic LYSO:Ce detector with dual-sided digital photon counter readout for ultrahigh-performance TOF-PET and TOF-PET/MRI

New applications for positron emission tomography (PET) and combined PET/magnetic resonance imaging (MRI) are currently emerging, for example in the fields of neurological, breast, and pediatric imaging. Such applications require improved image quality, reduced dose, shorter scanning times, and more precise quantification. This can be achieved by means of dedicated scanners based on ultrahigh-performance detectors, which should provide excellent spatial resolution, precise depth-of-interaction (DOI) estimation, outstanding time-of-flight (TOF) capability, and high detection efficiency. Here, we introduce such an ultrahigh-performance TOF/DOI PET detector, based on a 32 mm  ×  32 mm  ×  22 mm monolithic LYSO:Ce crystal. The 32 mm  ×  32 mm front and back faces of the crystal are coupled to a digital photon counter (DPC) array, in so-called dual-sided readout (DSR) configuration. The fully digital detector offers a spatial resolution of ~1.1 mm full width at half maximum (FWHM)/~1.2 mm mean absolute error, together with a DOI resolution of ~2.4 mm FWHM, an energy resolution of 10.2% FWHM, and a coincidence resolving time of 147 ps FWHM. The time resolution closely approaches the best results (135 ps FWHM) obtained to date with small crystals made from the same material coupled to the same DPC arrays, illustrating the excellent correction for optical and electronic transit time spreads that can be achieved in monolithic scintillators using maximum-likelihood techniques for estimating the time of interaction. The performance barely degrades for events with missing data (up to 6 out of 32 DPC dies missing), permitting the use of almost all events registered under realistic acquisition conditions. Moreover, the calibration procedures and computational methods used for position and time estimation follow recently made improvements that make them fast and practical, opening up realistic perspectives for using DSR monolithic scintillator detectors in TOF-PET and TOF-PET/MRI systems.

The use of 18F-FDG PET ratios in the differential diagnosis of common malignant brain tumors

OBJECTIVE

This study examined the use of positron emission tomography (PET) ratios to improve the diagnostic ability of 18F-FDG PET/computed tomography (CT) in the differentiation of enhancing brain metastases, central nervous system lymphomas, and gliomas.

MATERIALS AND METHODS

Seventy-six patients with malignant brain tumors and available magnetic resonance imaging and PET/CT examinations were included.

RESULTS

Among standardized uptake value (SUV)-related parameters tested, tumor maximum SUV to ipsilateral cortex maximum SUV ratio (Tmax:WMimax) and maximum SUV (SUVmax) proved to be the two most valuable parameters for differential diagnosis.

CONCLUSION

In addition to SUVmax, Tmax:WMimax also seems to provide helpful information for the differential diagnosis of lymphomas from other malignant brain tumors.